1. Field of the Invention
The present invention relates to a process for producing ethyl acetate, and more particularly, to a process for producing ethyl acetate by reacting ethylene with acetic acid in the presence of a catalyst.
Ethyl acetate may be used in a large amount for ethyl acetate coating materials, solvents, and starting material for producing various chemicals and industrial chemicals.
2. Description of the Related Art
As widely used industrial processes for producing ethyl acetate, heretofore there have been known a process comprising esterification of acetic acid with ethanol and a process comprising dimerization reaction of acetaldehyde in the presence of a metal alkoxide catalyst.
According to the production process using esterification, ethanol is used as a starting material in addition to acetic acid, and ethanol is commercially produced from ethylene for industrial use and therefore, is a secondary starting material. Moreover, ethanol is an expensive substance in Japan, Germany and others from the standpoint of national policy.
In addition, an esterification reaction is an equilibrium reaction so that it is necessary to remove co-produced water continuously from the reaction system by a certain method in order to achieve the high reaction conversion. These are problems concerning both starting materials and reaction efficiency. Therefore, there is much room for improvement.
According to the process involving dimerization of acetaldehyde (Tischtschenko reaction), the starting material, acetaldehyde, is a secondary starting material produced from ethylene. It is known that this dimerization reaction can proceed mildly and attain high conversion and selectivity.
However, a catalyst used in this reaction is usually a metal alkoxide such as aluminum alkoxide and the like, and the formation of acetaldol as a side reaction of the dimerization reaction and the subsequent dehydration reaction are inevitable. Water produced by the dehydration reaction easily decomposes the metal alkoxide catalyst. Therefore, this process suffers from problems as to the starting material and life of the catalsyt.
In view of the foregoing, as a new process for producing ethyl acetate, there have been recently researched vigorously a process for ethyl acetate starting from ethylene.
This process proceeds as a reaction of direct addition of ethylene to acetic acid and an acid catalyst is used.
For example, as a liquid phase catalytic reaction, Japanese Patent Application Laid-open No. 160745/1980 uses trifluoromethanesulfonic acid as a catalyst; Japanese Patent Publication No. 51060/1988 uses a metal cation-exchanged bentonite as a catalyst; and Japanese Patent Publication No. 30334/1981 uses a heteropoly acid of tungsten or its acidic metal salt soluble in the reaction media as a catalyst and a prescribed amount of water is added to the reaction system.
Among them, in the case of the process using a trifluoromethanesulfonic acid catalyst, the reaction results are good, but trifluoromethanesulfonic acid is expensive and very unstable and furthermore exhibits a very strong acidity. Therefore, this liquid phase homogeneous catalyst considerably corrodes reactors and the like.
Similarly, in the case of the process using a catalyst composed of a heteropoly acid of tungsten or its acidic metal salt which is a liquid phase uniform catalyst, corrosion occurs to a great extent and the catalytic activity is insufficient.
Further, though these liquid phase homogeneous catalysts can be easily separated from the product, ethyl acetate, it is very difficult to separate the liquid phase homogeneous catalysts from by-products formed during the reaction, in particular, high boiling point products. Therefore, recovery and regeneration of the catalysts are substantially not possible and as a result, the catalytic activity is disturbed and the life of catalyst is shortened.
In the case of the process using a catalyst composed of a metal cation-exchanged bentonite, a large amount of the catalyst should be used so as to achieve a high reaction yield and it is necessary to conduct the reaction at a temperature as high as 250.degree. C. In other words, there is a drawback that the catalytic activity is extremely low.
In view of the foregoing situation, from the standpoint of process, a method for producing ethyl acetate in a gas phase fixed bed has been recently researched vigorously aiming at advantages such as easy separation of the product from catalyst, easy continuous operation, and simplification of the reaction apparatus. For example, the following catalysts have been proposed for the above-mentioned purpose.
Japanese Patent Publication No.17775/1985 discloses the production of ethyl acetate by using a catalyst carrying aromatic sulfonic acids on a carrier such as silica and the like.
Japanese Patent Publication No. 17774/1985 discloses a catalyst carrying sulfuric acid or diethylsulfuric acid on a silica carrier.
Japanese Patent Publication No. 43384/1983 discloses a catalyst composed on a solid fluorine containing polymer having sulfonic acid group as side chain functional groups (e.g. Nafion).
Further, Kougyo Kagaku Zasshi, Vol.72 No.9,1945(1969) discloses the production of ethyl acetate by reacting acetic acid with ethylene in a gas phase in the presence of a silica-supported tungstosilicic acid catalyst and a strongly acidic cation exchanging resin catalyst.
However, these catalysts for gas phase reactions have many problems so that any of these catalysts have not yet been used in an actual industrial production.
For example, a silica-supported sulfonic acids, sulfuric acid, or diethylsulfuric acid catalyst suffers from intense volatilization and dissolving-away of the catalytic effective components during the reaction, and therefore, it is not possible substantially to carry out a continuous operation for a long time.
Further, Nafion catalyst is very expensive and in addition, the catalyst is not stable at a temperature (200.degree. C.) at which the reaction can be substantially carried out, and deterioration of the catalyst is inevitable.
Furthermore, catalytic activity of each of these catalysts is not sufficiently high and therefore, a very long reaction time is necessary when the reaction is effected at a low temperature and thereby the processes are not economical.
The tungstosilicic acid catalyst carried on silica and the strongly acidic cation exchange resin catalyst are not only of a low activity, but also the catalytic activity is lowered to a great extent within a very short time such as about two hours even at a temperature as low as about 150.degree. C. and deactivation of the catalyst is observed.
In view of the foregoing, conventional catalysts for the production of ethyl acetate by the addition of acetic acid to ethylene have verious problems whether the catalysts are liquid phase reaction catalysts or gas phase reaction catalysts. As a result, the process for producing ethyl acetate directly from ethylene and acetic acid has not yet been commercially employed.
Therefore, from as industrial point of view, there is demanded a catalyst for producing ethyl acetate from ethylene and acetic acid which can be simply used from the standpoint of process technique and has high durability and high reaction activity.